If your PC is > 4 years old, there's a good chance that the battery which keeps your BIOS chip content intact is fading, which is a common cause of BIOS settings starting to be lost. Hopefully it is a common "watch" type of battery which is coin shaped and readily available.
It would be worthwhile to painstakingly note down your BIOS settings (or print them off) so you can re-enter them after replacing your BIOS chip battery.
Generally speaking, once bad clusters start to appear on your hard disk, more is likely to follow. The unpredicable loss of data and loss of the use of your PC is painfully enough to give an urgent boost to you upgrading to a larger hard disk a.s.a.p.